A multicarrier communication system such as, e.g., Orthogonal Frequency Division Multiplexing (OFDM), Discrete Multi-tone (DMT) and the like, is typically characterized by a frequency band associated with a communication channel being divided into a number of smaller sub-bands (subcarriers herein). Communication of content (e.g., data, audio, video, etc.) between stations in a multicarrier communication system is performed by transmitting the content using a select one or more of a number of overlapping subcarriers. By overlapping the subcarriers, the total number of subcarriers is increased within a given bandwidth, with a corresponding increase in channel throughput. To maintain the interference immunity between such overlapping subcarriers, the subcarriers are controlled to be mathematically orthogonal to one another, e.g., wherein the peak of one subcarrier is positioned at a frequency that represents a substantial null to adjacent subcarriers.
Wireless communication systems and associated standards are using increasingly use more sophisticated modulation techniques such as 64 QAM and OFDM (orthogonal frequency division multiplex) to increase communication channel throughput. The increased sensitivity of these more sophisticated modulation techniques to small imbalances between the In-phase (I) and Quadrature (Q) paths of a low cost direct-conversion receiver and/or transmitter becomes a significant issue. Phase mismatch occurs when phase difference between local oscillator signal for the In-phase and Quadrature channels is not exactly 90 degrees. Gain mismatch between I and Q channels result from mixer, filters, or analog to digital converter (ADC) as well as non-uniformity between the channels. In addition, the IQ imbalance caused by I and Q arm filter mismatch is likely to also be a function of frequency. In this regard, IQ imbalance may have frequency independent components, frequency dependent components and may also introduce image interference aliasing into the desired signal band which may interfere with channel estimation.